1. Field of the Invention
The present invention relates to a lens drive device for a camera, and more particularly to a lens drive control device for a camera having an auto-focus function.
2. Related Background Art
A camera which drives an auto-focusing lens to an in-focus position with to an object has been known.
In such a camera having the auto-focus function, an in-focus state with respect to a target object is always maintained. However, the autop-focus device drives the lens after it has calculated the drive distance of the lens to reach the in-focus position. Accordingly, if the camera is directed from an object A; for which the lens is now in-focus, to an object B spaced from the object A, a certain time is required before the in-focus state for the object B is attained.
For example, during photographing of a baseball match having players such as a first base player, a pitcher and a field player, it may be required to photograph a runner who suddenly runs from a third base to home base. In such a case, a chance to photograph the runner may be lost because it is difficult to instantly attain the in-focus state with respect to the home base.
Japanese Patent Publication No. 40322/1981 discloses an approach to the above problem. In this method, a mechanical stop is provided on a lens barrel, and a distance ring of an imaging lens is matched to the home base to attain the in-focus state with respect to the home base; the distance ring is mechanically semi-fixed. Even if the distance ring is then moved, it can be manually returned to the semi-fixed position where it is mechanically stopped. In this method, however, it takes time to mechanically semi-fix the distance ring. Further, when this method is applied to an auto-focus camera, the response time is not significantly improved.
More specifically, if the lens is to be driven to the semi-fixed position while the lens is tracking the object in the auto-focus mode, the lens cannot be manually driven in the auto-focus mode. Thus, the mode must be first switched from the auto-focus mode to the manual mode, and then the lens barrel must be manually driven to the semi-fixed position. Since the switching from the auto-focus mode to the manual mode is required, the improvement of the response time is not attained.